High volume, low speed (HVLS) fans are large-diameter (e.g., 20 ft. diameter), ceiling-mounted fans that can be used to provide air flow in industrial and/or commercial buildings, warehouses, loading docks, etc. HVLS fans are typically suspended from the ceiling at heights from about 10 ft. to 35 ft. above the floor, and typically include a plurality of blades extending radially outwardly from a central hub. In operation, HVLS fans rotate at relatively low speeds to produce a large downdraft of air at relatively low speed to enhance the evaporative cooling effect on the skin of personnel within the airflow.
An advantage of HLVS fans is that the costs of installation and operation are often less than those of other types of air conditioning systems, such as forced air systems that provide cooling by changing the temperature of large volumes of air. A challenge, however, with current fan designs is that fan blades can deflect or “cone” at relatively higher speeds of rotation. Coning is the deflection of the set of fan blade out of the horizontal plane due to the lift encountered along the components of the blade. Coning reduces the ability of the fan to direct airflow in a direction perpendicular to the plane of the fan blades. This, in turn, reduces lift and the overall amount of air that flows directly toward the floor. These effects become more pronounced on longer fan blades because they are more flexible than shorter fan blades.
Another challenge with certain HLVS fans is that fan blade sections can have an aerodynamic center that is not aligned with the longitudinal centerline of the fan blade section. As a result, the fan blade section can encounter a differential or twisting load that twists the blade section along the longitudinal centerline. The twist of the fan blade section is more pronounced at the distal end of the blade section and can be positive or negative relative to the air flow. A positive twist can increase angle of attack and thereby increases drag. A negative twist can reduce the angle of attack and thereby reduce lift and the resultant amount of air flow. In addition to twisting loads, the fan blade sections of HLVS fan can produce a torque load that transmits through the blade section to the attachment system.